Neurological electrode system for magnetic resonance environments

ABSTRACT

An electrode system includes an electrode, a connector, and a cable with an in- line radio-frequency filter module comprising resistors and inductors without any deliberately added capacitance. The resistors are arranged in an alternating series of resistors and inductors, preferably with resistors at both outer ends, and connected electrically in series. The in-line module is located at a specific location along the wire, chosen through computer modeling and real-world testing for minimum transfer of received RF energy to a patient&#39;s skin, such as between 100 cm and 150 cm from the electrode end of a 240 centimeter cable. The total resistance of the resistors plus cable, connectors and solder is 1000 ohms or less; while the total inductance is roughly 1560 nanohenries. The inductors do not include ferrite or other magnetic material and are, together with the resistors, stock components thereby simplifying manufacture and reducing cost.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit andpriority of U.S. patent application Ser. No. 17/021,044, filed on Jan.15, 2020, entitled “NEUROLOGICAL MONITORING CABLE FOR MAGNETIC RESONANCEENVIRONMENTS” which further claims the benefit and priority of U.S.Provisional Patent Application No. 62/793,173, filed on Jan. 16, 2020,entitled “NEUROLOGICAL MONITORING CABLE FOR MAGNETIC RESONANCEENVIRONMENTS” the contents of which are herein incorporated byreference.

TECHNOLOGY FIELD

This disclosure relates to the use of electroencephalograph electrodesin magnetic resonance environments.

BACKGROUND

Electroencephalograph (EEG) electrodes are used in neurologicalmonitoring. An EEG electrode is part of a system that includes theelectrode, a cable and a connector. The electrode is attached to thepatient and picks up electrical signals in the brain or stimulatesnerves in the brain; the cable is attached to the electrode at one endand to an amplifier via the connector.

If the cable is in the presence of a magnetic field oscillating at aradio frequency (RF), such as that generated by a Magnetic ResonanceImaging (MRI) machine, the cable tends to act as an antenna and conductsthe radio frequency (RF) energy. The RF energy in the cable heats thecable and any electrically resistive material connected to it. If thecable is connected to an electrode attached to the skin of the patient,resistance heating at the skin-electrode interface may result in a burninjury.

MRI monitoring is a common hospital procedure, so procedures andprecautions are taken around MRI machines to avoid such injuries.Ironically, the stronger the magnetic field and the higher the radiofrequency, the better the image quality obtained from MR imagine butalso the greater the resistance heating and the potential for burns.

Because of the danger of MRI burns to a patient who requiresneurological monitoring and is to undergo MRI procedures, the electrodesare normally removed from the patient prior to the imaging procedure,and then re-attached afterwards. Attaching and re-attaching electrodesto patients is done by technicians, and the task is time-consuming andexpensive. Moreover, the patient is not being monitored when undergoingthe MRI procedure.

There are, however, electrode systems that may remain attached to thepatient's head during MR imaging subject to conditions. These electrodesystems are typically referred to as “MRI-conditional.” The conditionson use of these electrodes may include limits on the strength of themagnetic field of the MR imaging device and the time the patient mayremain in the magnetic field attached these electrode systems. MRIconditional electrode systems may use different materials that respondless to magnetic fields, for example, or use tank filters(inductor-capacitor circuits) inserted into the electrode cables toblock unwanted RF energy. Unfortunately, tank filters arefrequency-specific, so they are not always effective in reducing heatingwhen used in MRI machines. The need to tune these filters individuallyto the precise frequencies used in MRI also makes them relatively costlyand labor-intensive to build.

As a result, there continues to be a need for better ways to avoid orminimize RF heating in electrode systems attached to the patient duringMR imaging.

SUMMARY

According to its major aspects and briefly recited, it has been foundthat a combination of inductors and resistors inserted in-line at anoptimal position in the cable of the electrode system forms a radiofrequency filter that reduces heating and is less frequency-specificthan a tank filter.

An aspect of the disclosure is that the components of the presentin-line filter do not include tank filters with their need for precisetuning.

An aspect of the disclosure is that the values and numbers of theresistors and inductors for the in-line filter are selected to reduceradio frequency (RF) power in the electrode system and especially heatdissipation into the skin beneath and near the electrodes.

An aspect of the disclosure is that the values and arrangement ofcomponents for the in-line filter are selected to reduce RF power in theelectrode system, and reduce excessive heating, through an alternatingrelationship of resistors and inductors.

Another aspect of the disclosure is that the choice of location in thecable for the in-line components is selected to reduce RF power in thatelectrode system.

An aspect of the disclosure is that the choices of location, the numbersand component types and values, and arrangement for the in-line RFfilter in the cable are selected to reduce the RF power over a broadrange of radio frequencies.

Another aspect of the disclosure is that the components of the in-lineRF filter may be stock-valued components.

An aspect of the disclosure is that the present RF filter is comprisedof miniature, leadless surface-mountable components enclosed bybiocompatible, electrically-insulating material comprising a smallin-line filter module.

Another aspect of the disclosure is that all module materials and filtercomponents are chosen to contain either no magnetic material at all, orat least the minimum feasible quantity of such material including nickelplating, thus minimizing the risk of dangerous attraction in very strongmagnetic fields.

An aspect of the disclosure is the use of approximately 1000 ohms ofresistance or less in the present RF filter, as required for optimalperformance in a typical EEG amplifier.

Another aspect of the disclosure is the use of ferrite-free inductors inthe

RF filter, thus minimizing not only the risk of dangerous attraction butalso that of magnetic saturation altering the properties of ferrites instrong magnetic fields.

Another aspect of the disclosure is that the total inductance of thein-line RF filter may lie between one and two microhenries, readilyachieved without the use of magnetic material.

An aspect of the disclosure is an RF filter included in a neurologicalelectrode system having at least one resistor in series with at leastone inductor in-line in the RF filter.

Another aspect of the disclosure is that the components are constructedas a miniature filter module for in-line use in the electrode cable.

Still another aspect of the disclosure is that for a designed in-linefilter module located between the first end and the second end of saidcable, at a location found by antenna system simulation in software andthen improved through a modest amount of real-world experimentation, atleast one improved location of said filter module will reduce thecoupling of RF energy into the skin of the patient, thus reducing thedanger of burns.

Still another aspect of the disclosure is that, for cables within therange of 240 millimeters to 1000 millimeters (one meter) inclusive andusing the miniature filter model described in an embodiment of the radiofrequency attenuator, the improved location may be determined using asimple mathematical formula.

An aspect of the disclosure is that the in-line filter module maycontain an alternating and substantially linear arrangement of resistorsand inductors electrically connected in series.

Another aspect of the disclosure is that resistance, and thus powerdissipation, in the in-line RF filter is divided among a multiplicity ofresistors all having the same or closely similar stock values, thusfurther reducing heat dissipation at any one location along the filter.

Still another aspect of the disclosure is that the needed inductance inthe in-line RF filter is achieved using a multiplicity of ferrite-freeinductors, all having the same or closely similar stock values, andfurther acting as spacers between the heat-generating resistors.

Another aspect of the disclosure is that the number of resistorsdesirably exceeds the number of inductors by one, so resistors appear atboth ends of the linear arrangement. In other words, if a number N offerrite-free inductors is required to achieve the needed totalinductance, the number of resistors will desirably be N+1.

An aspect of the disclosure is that the in-line filter module hascontacts on the ends to connect the in-line filter module with thecable. These contacts are preferably comprised of, or at least platedwith, copper, silver or gold avoiding the use of nickel or othermagnetic materials. Since the wire comprising the cable is likely to bemade of carbon fibers instead of copper, and thus not solderable, tin orsolder plating is not desirable.

These and other aspects of the disclosure and their features andadvantages will be apparent to those skilled in the art of neurologicalmonitoring from a careful reading of the Detailed Description,accompanied by the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an electrode system including an in-line RFfilter module, according to an aspect of the disclosure;

FIG. 2 is an end view of a cross section of the in-line RF filter moduleof FIG. 1;

FIG. 3 is a side perspective view of a double-sided printed circuitboard designed for enclosure by the in-line module of FIG. 1, showing anexample of the components used therein, according to an aspect of thedisclosure;

FIG. 4 is a plan view of an alternative, single-sided printed circuitboard designed for enclosure by the in-line module of FIG. 1, showing anexample of the components used therein, according to an aspect of thedisclosure;

FIG. 5 is an electronic schematic diagram of the filter module accordingto an aspect of the disclosure;

FIG. 6 is a graph of RF power delivered to a patient's skin for threedifferent magnetic resonance radio frequencies when using a simulatedin-line filter module placed in one of various locations along a240-millimeter cable of an electrode system, according to an aspect ofthe disclosure; and,

FIG. 7 is a graph of RF power delivered to a patient's skin at amagnetic resonance radio frequency of 128 MHz, such as used in 3-TeslaMRI machines, placed along cables measuring 240, 300, 500, 700 and 1000millimeters in length, respectively.

DISCUSSION OF THE PRIOR ART

An examination of the prior art in this field showed many U.S. patentsalready exist, including U.S. Pat. Nos. 7,945,322; 8,116,862; 8,180,448;8,200,328; 8,301,243; 8,311,628; 8,463,375, 8,649,857 and 9,061,139) allby the same inventors (Stevenson et al.) and having the same objectiveof creating implantable devices using tank circuits to block specificundesirable frequencies.

A tank circuit is the parallel combination of an inductor (unavoidablyincluding some resistance) with a capacitor, which may be discrete suchas a manufactured chip or film capacitor or may include othercapacitance contributed by nearby objects such as traces or copper areasleft on a printed-circuit board. It blocks a typically narrow frequencyrange centered on fc=1|2n (LC), its resonant center frequency, where fcis the frequency in hertz, L the inductance in henries, and C thecapacitance in farads.

For example, an inductor with a value of 390 nanohenries (“L”) and aten-picofarad capacitor (“C”) yield fc=80.6 megahertz, close to the FMbroadcast band.

The effect of resistance in the tank is to change a parameter “Q,” whichbecomes lower as the resistance increases. High “Q” makes the tank avery effective barrier at fc, with performance falling off sharply asthe frequency deviates from it. Low “Q” broadens the frequency response,but at the expense of performance close to fc.

Because it is difficult to control the values of inductors andcapacitors precisely, and account for stray capacitance and the effectof magnetic materials in the environment around a tank circuit, somedegree of individual adjustment is usually needed to make each tankresonate at the desired fc. This requires the use of tunable components,such as adjustable capacitors, which are far more costly than stockfixed-value ones. The tank must then be isolated from outside effects,which could affect its tuning. In production, this typically addssignificant cost. As a further disadvantage, the tank will then blockonly that one frequency (and a narrow band of others near it) whilehaving little or no effect at others.

The prime object of the invention, therefore, is to provide a barrieragainst RF energy in EEG electrode leads which avoids the disadvantagesof tank circuits by taking a wholly different approach: eliminating theuse of parallel capacitance; treating the full electrode, cable andconnector together as an antenna-like system at all typically-used MRIradio frequencies; and in that system placing in an optimal positionalong each cable a filter module comprising lumped inductance andresistance forming a non-resonant filter effective at more than one suchfrequency, the optimal position being that which causes a minimum amountof RF energy to be delivered to the skin of a patient in contact withthe electrode thereby minimizing the danger of burns.

Another object is to provide this RF energy barrier using componentsable to be used safely in an MRI environment, in the sense of being “MRIconditional” with field strengths and other conditions specified asneeded.

A third object is to provide the MRI-compatible barrier using onlylow-cost, widely-available, stock-valued components requiring noindividual adjustment after assembly.

A fourth object is to provide the barrier in the form of a compactfilter module which can be mounted in-line in the electrode cables andbe safe for use in a medical environment.

A fifth object is to make such a module, and thereby the electrodesystem containing it, more tolerant of radio-frequency energy and robustagainst resistance heating than the prior-art electrode systems.

DETAILED DESCRIPTION OF THE INVENTION

A computer model was developed for a set of neurological monitoringelectrodes to evaluate RF pickup from an RF device. The model wasdeveloped using the commercially-available EZNEC+, Version 6.0 antennamodeling software.

For this model, the electrodes, wires, connectors, and the patient'shead are represented as parts of a radio-frequency receiving antenna.The patient's head is divided into nineteen conductive volumes, eachwith its own resistance and capacitance, to simulate the distribution ofradio-frequency current through an extended, electrically resistive loadvia the skin effect. The external cables are represented by straightwires, dangling wires, or a loop that includes a capacitor representinga multi-electrode connector.

Loads, simulated by two 3000-ohm resistors, simulate the typicalresistance between the skin and each electrode. Additional loads, eachcomprised of inductance and resistance, are modeled in a way permittingeasy relocation along the wires to simulate filter modules placed invarying locations.

To simulate the rotating RF field around a patient undergoing MRImaging, the “birdcage” coil used as an RF source in a typical MRImachine was modeled as a set of four interconnected source dipoles, eachdipole being 90 degrees out of phase with the next.

Referring now to FIGS. 1-5, FIG. 1 shows an electrode system 10including an electrode 14, a cable 18 with an in-line filter module 22,and a connector 26. Cable 18 is in electrical connection with electrode14 and with connector 26. Electrode 14 may be attached to the head of apatient along with other electrodes for neurological monitoring or otherneurological procedure. Connector 26 along with other connectors ofother cables are connected to an amplifier (not shown) to amplify thesignals received from electrode 14 and which signals traveled throughcable 18 and in-line filter module 22.

A cross-sectional view of in-line filter module 22, cut along line 2-2in FIG. 1, is shown in FIG. 2. In-line module 22 includes a housing 56made from a tough, electrically nonconductive and nontoxic polymer suchas epoxy, silicone rubber, polyvinyl chloride, polyethylene orpolypropylene. Housing 56 contains and protects a substrate 30, such asa small printed-circuit board, which is shown in perspective in FIG. 3,to which are attached plural resistors 34 alternatingly in series withplural inductors 38. Substrate 30 is inserted in-line in cable 18 socable 18 is electrically connected to both ends of substrate 30 atcontact pad 46, 46′, with solder, conductive epoxy, graphite-paste “wireglue” or other suitable connecting material 50, 50′. Substrate 30, andthereby in-line filter module 22 is thus in electrical connection withelectrode 14 and connector 26.

In FIGS. 3 and 4, resistors 34 and inductors 38 are shown as they mightbe mounted on two different types of printed circuit boards:double-sided in FIG. 3 and single-sided in FIG. 4. In each case thenumber of inductors “N” is four, so the number of resistors “N+1” in analternating set: resistor 34, inductor 38, resistor 34, inductor 38, andso forth, with all resistors and inductors connected electrically inseries. In FIG. 3, the inductors and resistors are placed on oppositesides and connected through vias, while in FIG. 4 all components are onthe same side of the board. The latter approach simplifies construction,though at the cost of an increase in overall width.

In any manufacturer's series of standard miniature surface-mountinductors, those with higher inductance values have cores made offerrite, a magnetic ceramic, while lower-valued ones use nonmagneticceramics such as porcelain or alumina. Typically, 390 nanohenries (0.39microhenries) is the largest value currently made without a ferritecore.

Although comprised chiefly of iron oxide, ferrites come in manycompositions optimized for different frequency ranges. They respondstrongly to magnetic fields, both by experiencing physical force and byundergoing magnetic saturation which, if the ferrite is used in aninductor, will change the inductor's value. Accordingly, ferrite coresshould be avoided in inductors meant for use in strong magnetic fieldsor near devices, such as MRI equipment, generating them.

In simulation, values of inductance found usable for the invention werein the range of one to two microhenries with an optimal value around1.56 microhenries (1560 nanohenries). This value is easily achieved byconnecting four ferrite-free, off-the-shelf 390-nanohenry miniatureinductors electrically in series.

It is convenient for manufacturing, although otherwise not strictlynecessary, to make inductors 38 all have the same nominal value andmanufacturer's part number. For a total inductance of 1.56 microhenries,divided among four inductors as shown in FIGS. 3, 4 and 5, this nominalvalue, as just stated, is 390 nanohenries.

It should be stressed that nominal values include some error and aretypically given with tolerances of ±1%, ±5% or the like, so an inductorsold as “390 nanohenries±5%” might have an actual value lying anywherefrom 370.5 to

409.5 nanohenries. Differences of this order are often critical to thecorrect operation of tank circuits, but in the present design shouldmake little difference.

The nominal values of each component type most often manufactured,usually standardized among manufacturers, are known as stock values. 390nanohenries is an example of such a stock value. It is possible thatinductors with different stock values than 390 nanohenries may in somecases be found more convenient to use. For example, advances inminiature inductor technology may yield higher inductance values withoutusing ferrite, thus permitting a needed value to be achieved using asmaller number of physically discrete inductors.

Inductors 38 should be physically spaced a small distance apart so theirmagnetic fields do not overlap significantly. Such overlap, and theresulting interaction between their fields, could change their effectivetotal inductance. Spacing is conveniently achieved by setting themphysically apart in an alternating arrangement with the resistors, asshown in FIGS. 3 and 4. Conveniently, the physically adjacent devicesare then connected electrically, again alternating between inductors andresistors, as shown schematically in FIG. 5.

Such an alternating arrangement has the additional advantage ofdistributing the heat from RF power dissipation in the resistors aswidely as possible along the length of the filter module, minimizingpotential hot spots. For the latter reason, and since chip resistors aremuch less costly than miniature inductors, it is desirable- although notstrictly necessary- to have one more resistor (“N+1”)than inductor (“N”)as shown in FIGS. 3, 4 and 5, thus distributing any generated heat morewidely.

Resistors may be selected to have a cumulative resistance of up to 1000ohms, thus remaining within the input requirements for reliableoperation of most EEG amplifiers. To allow for resistance in the cable,connections and the inductors themselves, however, it is desirable tomake the actual total resistance within the filter module lower.Depending upon the values of those other resistances, a total resistanceas low as 1 ohm within the filter module may be found usable.

Just as with the inductors it is convenient for manufacturing, althoughotherwise not strictly necessary, to make resistors 34 all have the samenominal or stock value and manufacturer's part number.

For example, in a preferred embodiment a filter containing four (“N”)390-nanohenry inductors built according to this invention would includefive (“N+1”) resistors. Dividing 1000 ohms by five yields 200 ohms. Thenext few ±1% stock resistor values below 200 ohms are 196, 191, 187, 182and 180 ohms. One of these values, or possibly one still lower if otherresistances in the system are expected to be high, should be selectedand may then be optimized by a modest amount of experiment.

A concrete example of in-line filter module 22 according to thepreferred embodiment thus includes five resistors 34 each having aresistance of 180 ohms, and four ferrite-free inductors each having aninductance of 0.39 microhenries, arranged in alternation and connectedin series beginning and ending with a resistor 34. The complete modulethus has a resistance of 900 ohms in series with 1.56 microhenries.

Simulation of the effectiveness of this in-line filter in a cable 18between an electrode 14 and a connector 26, and exposed to threedifferent commonly-used magnetic resonance frequencies, produced theresponse curves shown in FIG. 6 as a functions of the location ofin-line module 22, embodying the concrete example given, along a cable18 that is 240 mm long. The horizontal axis represents the distancealong the wire from the electrode end, while the vertical axis shows thepower delivered to a simulated skin resistance directly under theelectrode. To avoid potential burns to the patient, as stated earlier,the prime object of the invention is to minimize this power.

Curve 50, with calculated data points indicated by triangles, shows thedelivered power at 64 MHz while for comparison horizontal dashed line 52shows a constant 8.8 milliwatts, the power with no filter modulepresent. Given that the 240-millimeter wire occupies only 5% of the4.65-meter wavelength of the 64-MHz RF energy, it functions very poorlyas an antenna. Hence, the received and delivered power levels are lowand adding the filter module makes little difference. RF burns have beenof little concern with 1.5-Tesla MRI machines, which use 64 MHz as theRF frequency.

Increasing the magnetic field strength in an MRI machine improves theimage quality and resolution, and to maintain resonance, the RFfrequency is increased in proportion. Most new MRI machines operate atthree Tesla, requiring a frequency of 128 MHz with a correspondingwavelength of 2.33 meters. Here the 240-millimeter wire occupies about10% of the 2.33-meter wavelength, functioning much better as an antenna.This raises a definite concern of injury to a patient from RF energy.

Curve 54 shows the delivered power, while again for comparison dashedline 56 shows the power with no filter module present. As is readilyseen, with no filtering the power at 128 MHz, 43.8 milliwatts, is nearlyfive times what was seen at 64 MHz.

At 128 MHz a filter module according to the preferred embodiment now hasa strong effect on the delivered power, either raising or lowering itdepending on the module's position. The region in which the module canbe located to reduce the delivered power is surprisingly broad comparedto the wire's length, and the amount of reduction at the minimum pointis very substantial. For example, in a 240-millimeter wire, the minimumoccurs with the module about 190 millimeters from the electrode, withdelivered power of just 2.56 milliwatts: only 6% of the value withoutthe module present.

Experimental MRI machines now in development use still stronger magneticfields, typically of seven Tesla thus requiring an RF frequency of 299MHz. Since at this frequency the 240-millimeter wire is nearlyone-quarter wavelength, it picks up RF energy very efficiently.

Curve 58 shows a part of the resulting delivered power response, whichextends far off the top of the chart at both ends. The power levelwithout filtering, 3.18 watts, cannot be shown for comparison withoutexpanding the graph and could easily be enough to cause serious injuryto a patient. Installing the preferred embodiment of the filter module80 millimeters from the electrode substantially reduces this power levelto just 0.48 milliwatt: 0.015% of the unfiltered value.

FIG. 7 shows the same curves for the three-Tesla frequency of 128 MHzonly, for varying lengths of wire measuring 240, 300, 500, 700 and 1000millimeters in length, respectively. Wires 18 a-18 e are depicted toscale, with electrodes 14 a-14 e at left and connectors 26 a-26 e atright.

Curve 54 a reproduces curve 54 in FIG. 6 for the 240-millimeter wireshowing power dissipated at the patient's skin as a function of thelocation of filter module 22, while dashed curve 56 a reproduces line 56showing the power with no filtering. Curves 54 b, 54 c, 54 d and 54 e,and dashed curves 56 b, 56 c, 56 d and 56 e, show the correspondingpower curves and unfiltered power levels in the 300-, 500-, 700- and1000-millimeter wires respectively.

As can be seen in FIG. 7, for each power curve a broad minimum appears,containing within it a point 74 a, 74 b, 74 c, 74 d or 74 e at which thedelivered power is minimized. For curves 74 d and 74 e, representing thedelivered power for the 700- and 1000-millimeter wires, a dashed line 74d′ or 74 e′ has been added magnifying a portion of each curve to showthe minimum more clearly.

If filter modules 22 a, 22 b and so forth are drawn on each wire 18 a,18 b and so forth in their correct positions for minimizing thedelivered power, it can be seen from FIG. 7 that they fall very nearlyon a straight line 80. The slight discrepancy may be due to the finiteresolution (“segmentation”) of the EZNEC antenna modeling software.

For the concrete example described above, 900 ohms in series with 1.56microhenries, used at a radio frequency of 128 megahertz, line 80represents an optimum location for filter module 22 of LM=0.27 L+135,where L is the total length of the electrode system 10, LM is thedistance from electrode 14 to the center of module 22, and all distancesare expressed in millimeters. Similar formulas can probably be derivedfor filter modules containing other values of resistance and inductance.

It should be stressed, however, that since computer simulation requiredsome simplifying assumptions the real-life measured curves will likelydiffer slightly from those shown. Optimization may then be obtained bymodest experimentation that is well within the capability of those ofordinary skill in the art.

A series combination of inductors and resistors, without capacitors,when inserted into the cable of the electrode system in the form, forexample, of an in-line filter module, forms an effective RF filter thatreduces resistance heating at the patient's skin surface under and nearthe electrodes while being less frequency-specific than a tank filter,able to be made with stock off-the-shelf components, and requiring noindividual tuning after assembly.

Optimizing in-line filter module 22 through experimentation on thenumber and value of the components, which are resistors 34 and inductors38, and no capacitors; through favoring stock values for resistors 34and inductors 38; and through favoring positions for in-line module 22between the ends of cable 18, and generally toward the middle of a 250centimeter cable; may provide an MRI cable 18 for electrode system 10that has far fewer restrictions and is more tolerant of radio-frequencyenergy and robust against resistance heating than prior art electrodesystems.

What is claimed is:
 1. A neurological electrode system for use inmagnetic resonance environments, comprising: a magnetic resonanceenvironment with a radio frequency (RF) field; an electrode forneurological monitoring; a connector configured to connect to anamplifier; a cable, having a first end and a second end, the first endin electrical connection to the electrode, the second end in electricalconnection to the connector; and an inline filter module configuredalong the cable, the inline filter module comprises one or moreresistors and one or more inductors configured in series, wherein totalresistance of the one or more resistors is below 1 ohm, and the inlinefilter module limits heat generation in the electrode.
 2. The system ofclaim 1, further comprising two or more inline filter modules configuredalong the cable.
 3. The system of claim 1, further comprising an inlinefilter module placed between 40 to 80 millimeters along the cable fromthe electrode.
 4. The system of claim 1, further comprising an inlinefilter module placed between 80 to 120 millimeters along the cable fromthe electrode.
 5. The system of claim 1, further comprising an inlinefilter module placed between 120 to 160 millimeters along the cable fromthe electrode.
 6. The system of claim 1, further comprising the one ormore inductors as a number N of inductors, and further comprising theone or more resistors as a number N+1 of resistors.
 7. The system ofclaim 1, further comprising the one or more inductors spaced a smalldistance apart and the cable itself is the one or more resistors.
 8. Thesystem of claim 1, further comprising having more than one resistor inthe one or more resistors, each of the resistors possessing the sameresistance as the other resistors.
 9. The system of claim 1, furthercomprising having more than one inductor in the one or more inductors,each of the inductors possessing the same inductance as the otherinductors.
 10. The system of claim 1, further comprising the one or moreinductors having a total inductance between 1 and 2 microhenries. 11.The system of claim 1, further comprising the one or more inductorshaving a total inductance between 1370 and 1800 nanohenries.
 12. Thesystem of claim 1, further comprising the one or more resistors having atotal resistance between 0.1 and 1000 ohms.
 13. The system of claim 1,further comprising the one or more resistors and the one or moreinductors being substantially linear on the cable and electricallyconnected in series.
 14. A neurological monitoring apparatus formagnetic resonance environments, comprising: a neurological electrode,the neurological electrode in electrical communication with neurologicalelectrical signals; a connector operatively configured to an amplifier;a cable having a distal end connecting to the neurological electrode,and a proximal end configured to the connector; and an inline filtermodule, the inline filter module limits heat generation at theneurological electrode from radio frequency energy, by an alternatingseries of one or more resistors, and one or more inductors, wherein theone or more resistors and the one or more inductors are in asubstantially linear arrangement on the cable.
 15. The apparatus ofclaim 14, further comprising the one or more inductors as ferrite-freeinductors.
 16. The apparatus of claim 14, further comprising the one ormore inductors as having a number N of inductors, and the one or moreresistors as having a number N+1 of resistors.
 17. The apparatus ofclaim 14, further comprising the one or more inductors spaced a smalldistance apart and the cable itself is the one or more resistors. 18.The apparatus of claim 14, further comprising having more than oneresistor in the one or more resistors, each of the resistors possessingthe same resistance as the other resistors.
 19. The apparatus of claim14, further comprising having more than one inductor in the one or moreinductors, each of the inductors possessing the same inductance as theother inductors.
 20. The apparatus of claim 14, further comprising aninline filter module, wherein the inline filter module is between 1 and2 microhenries.
 21. The apparatus of claim 14, further comprising theinline filter module being located near midpoint or center of the cable,from the distal end and the proximal end.